It occurs to me that MathML should probably play a key role here, as it is a W3C Recommendation for integrating mathematical content into web documents. A matrix like I described should certainly qualify. As an added bonus, any client software that understands MathML would immediately recognize my covariance matrix as a matrix in the mathematical sense, whether or not it can pull other semantic meaning from the document. It would still be nice to use a microformat to convey some more semantic meaning. I'm not sure if I could say in MathML that my matrix is a covariance matrix. And I seriously doubt I would be able to convey that it describes measurement uncertainty on a geographic location. So... can I use class attributes here? MathML tags are not XHTML tags, after all. Is it legal to apply the concepts of microformats to other xml vocabularies embedded in an XHTML document? Or maybe, whether the above is allowed or not, it would be preferable to use a class attribute in a containing element, such as a div or span, so that the class attribute is kept out of non-html tags. And if that is the case, can I declare that to conform to my microformat, an element with a given class (say, "covariance") must contain a mathml:mtable element? <div>On 7/30/07, Andy Mabbett <<a href="mailto:andy@pigsonthewing.org.uk" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">andy@pigsonthewing.org.uk </a>> wrote:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> In message <<a href="mailto:5887c53f0707301336p73c6befbu823058abfcc98ea8@mail.gmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">5887c53f0707301336p73c6befbu823058abfcc98ea8@mail.gmail.com </a>>, Charlie <<a href="mailto:microformats@charlie.okeefe.name" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> microformats@charlie.okeefe.name</a>> writes >I would love to hear people's thoughts on how to design such a format! I'm not sure what we should do... -- Andy Mabbett _______________________________________________ microformats-new mailing list <a href="mailto:microformats-new@microformats.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">microformats-new@microformats.org</a> <a href="http://microformats.org/mailman/listinfo/microformats-new" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> http://microformats.org/mailman/listinfo/microformats-new </a> </blockquote></div>